Mineral fiber composition

ABSTRACT

A mineral fiber composition which is soluble in biological fluids contains substantially 
     45-65% by weight of SiO 2    
     15-40% by weight of CaO 
     0-20% by weight of MgO 
     0-6% by weight of Na 2 O+K 2 O 
     and in addition aluminium and/or iron oxides as well as phosphorus oxide in such amounts that the weight ratio of P 2 O 5  to the sum of Al 2 O 3  and iron oxide is circa 0.4 to 6.

This is a continuation of application Ser. No. 08/444,543, filed May 19, 1995 U.S. Pat. No. 5,843,854, abandoned which is a continuation of application Ser. No. 07/849,384, filed May 7, 1992, which is a 35 U.S.C. §371 of International PCT application Ser. No. PCT/FI91/00349, filed Nov. 22, 1991.

The present invention relates to a mineral fiber composition which is soluble in biological fluids.

BACKGROUND OF THE INVENTION

Mineral fibers made by melting and spinning of mineral raw materials, such as rock, slag and the like, are to a great extent used for the manufacture of mineral fiber mats and blankets, primarily for heat and sound insulation purposes within the construction industry. In addition to the formed mat exhibiting good insulation characteristics with respect to heat and sound, increasingly more importance has been recently attached to the characteristics of the mat from the viewpoint of health, primarily of industrial hygiene. This has lead to attention being directed increasingly more to developing fiber which are soluble in biological fluids in order to ensure that fiber particles, which are not transported out of the body, dissolve in the body fluid.

Thus e.g. the patent application WO 89/12032 describes a fiber composition which exhibits an increased solubility in physiological saline solutions. According to the specification, the components in the said compositions may vary within wide limits, but according to the specification, an increase in the amount of amphoteric oxides, i.e. of aluminium, zirconium and titanium, tends to increase the stability of the compositions against extraction. Even though the application does not at all discuss the effects of the presence of phosphorus, there is included an example of a composition containing a little over 6% by weight of P₂O₅, in combination with a low content of Al₂O₃. This composition exhibits a fairly good solubility, primarily due to the small amount of Al₂O₃ present.

According to the present invention it has now been discovered that compositions which contain aluminium and/or iron oxides, as well as phosphorus oxide, and wherein the weight ratio of phosphorus to the sum of aluminium and iron, all calculated as their oxides, lies within a fairly narrow range, surprisingly exhibit very favourable solubility characteristics in physiological saline solutions.

The object of the present invention is thus a mineral fiber composition which is soluble in biological fluids and which is characterized in that it contains substantially

45-65% by weight of SiO₂

15-40% by weight of CaO

0-20% by weight of MgO

0-6% by weight of Na₂O+K₂O

and in addition aluminium and/or iron oxides as well as phosphorus oxide in such amounts that the weight ratio of P₂O₅ to the sum of Al₂O₃ and iron oxide is circa 0.4 to 6.

The total amount of Al₂O₃ and iron oxide is preferably at least circa 0.5, advantageously circa 0.5 to 7% by weight and the weight ratio is preferably circa 0.5 to 2.

The object of the invention is also a method for increasing the solubility of mineral fiber compositions which method is characterized in that to a mineral composition having a total Al₂O₃ and iron oxide content of at least circa 0.5% by weight, phosphorus is added in such an amount that the weight ratio of P₂O₅ to the sum of Al₂O₃, and iron oxide is circa 0.4 to 6, optimally circa 0.5 to 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention thus makes it possible to utilize such common natural and economically feasible raw materials which generally contain a certain amount of aluminium and iron, which reduce the solubility and the presence of which consequently is not desirable in the manufacture of a soluble fiber. According to the invention the solubility of fibers made from such materials is increased by adding phosphorus in a suitable amount. This increases substantially the variation possibilities in the choice of raw materials whereby also economically advantageous raw materials can come into use.

The upper limit of added phosphorus oxide, which generally does not exceed circa 10% by weight of the composition, depends naturally on the aluminium and iron content and also on the fact that higher phosphorus oxide, levels contribute to an undesired crystallization of the fiber and difficulties in raw material supply. An increase of the phosphorus oxide content also raises the melting temperature which leads to even poorer production economics.

In order for mineral fibers to be bioactive or soluble in biological fluids, a layer of calcium phosphate or apatite type material is required on the surface of the fiber. This outer layer is a result of migration of calcium and phosphate ions from the glass matrix outwards to the surface directed towards the biological fluid, which surface layer formation is further facilitated by the phosphate ions present in the biological fluid.

This formed layer gradually then separates in the form of very small particles thus exposing new fiber surface onto which new surface layers then can form. The glass matrix gradually being leached, the fiber disintegrates and disappears.

The presence of trivalent aluminium and iron has a stabilizing effect on the leaching of the glass matrix due to the fact that these metals tend to move to disrupted oxygen bridges in the glass, where the deterioration and leaching reactions of the glass take place. The phosphate ions, however, form complexes with these trivalent metal ions and weaken the oxygen bridges between the Si— and Al— and Fe— atoms, respectively. As a consequence of this, the network forming properties of these metals weaken in turn, which facilitates the breaking down of the glass.

The present invention is consequently based on a joint effect between phosphate and aluminium and trivalent iron, respectively, which cooperation in the mineral fibers according to the invention increases the solubility of the fiber.

In the following, when iron oxide is expressed as Fe₂O₃, this expression is intended to cover all types of iron oxides Fe_(x)O_(y) present in the composition.

An advantageous fiberizable mineral fiber composition contains the following components at the amounts indicated:

SiO₂ 45-65% by weight Al₂O₃ 0.5-7% by weight Fe₂O₃ 0-5% by weight CaO 15-40% by weight MgO 0-20% by weight Na₂O + 0-6% by weight K₂O P₂O₅ 0.5-10% by weight

An especially advantageous composition has the following composition:

SiO₂ 49-56% by weight Al₂O₃ 1-5% by weight Fe₂O₃ 0-4% by weight CaO 25-35% by weight MgO 0-15% by weight Na₂O + 0-6% by weight K₂O P₂O₅ 0.5-5% by weight

Solubility Tests

1. Solubility in a Gamble Solution

In order to test the solubility, mineral fiber compositions according to the invention were compared with corresponding compositions which, however, contained no phosphate.

From quartz sand, calcium carbonate, Al—, Mg— and P— compounds a melt was prepared which after solidification was crushed and pulverized. The chemical composition was controlled, as was the particle size distribution. A specimen of 200 ml was rinsed with a Gamble solution having a flow rate of 2 ml/h. The Gamble solution had the following composition:

MgCl₂ * 6H₂O 0.16 g/l NaCl 6.11 g/l KCl 0.31 g/l Na₂HPO₄ 0.148 g/l Na₂SO₄ 0.079 g/l CaCl₂ * 2H₂O 0.06 g/l NaCH₃COO * 3H₂O 1.065 g/l NaHCO₃ 1.95 g/l

The rate of dissolution was determined by measuring the concentrations of the main components of the material in the Gamble solution after specific time intervals. An atomic absorption spectroohotometer was used for the determinations.

Composition (% by weight) Ia Ib IIa IIb SiO₂ 55.2 58.8 54.1 54.2 Al₂O₃ 1.2 1.2 4.2 4.4 Fe₂O₃ 0.1 0.05 0.05 0.0 CaO 29.3 30.2 27.7 30.2 MgO 10.2 9.7 9.7 10.4 Na₂O 0.1 0.03 0.09 0.1 K₂O 0.0 0.02 0.02 0.02 P₂O₅ 1.7 — 3.9 —

Solubility (ma/l) (1 day) Ia Ib IIa IIb Si 62.2 58.6 34.5 32.1 Ca 27.8 27.7 22.7 30.3 Mg 16.5 14.0 13.4 14.5

From the results it can be seen that the compositions Ia and IIa according to the invention which contained phosphate, had a better silicon solubility than the corresponding compositions lb and IIb which were phosphate free. Magnesium and calcium solubilities remained rather constant.

2. Solubility in Culture Media with or without Macrophages

In this test the dissolution, of three mineral fiber compositions were tested on the one hand in a commercial culture medium (RPMI 1640 Medium, Gibco Ltd, England) and also in the same culture medium containing in addition macrophages. The latter medium was prepared by suspending rat alveolar macrophages, the viability of which was over 95%, in a RPMI 1640 medium containing pencillin 100 IU/ml, streptomycin 100 μg/ml, 10 IU/ml heparin, 10% foetal calf serum and 2 mM L-glutamine, to a cell concentration of 1×10⁶ cells/ml. 2 ml of cell suspension was added to and incubated in each well of Costar tissue culture clusters (Costar Europe Ltd, Holland), changing the medium to remove non-adherent cells, and incubated overnight. Following incubation, the medium was removed and fresh medium containing 200 μg/ml of mineral fibers were added to the wells. In control wells, only RPMI 1640 Medium with 200 μg/ml of mineral fiber was used. The clusters were incubated and the cells exposed to fibers for a predetermined time. The concentration of dissolved silicon from each of the samples was determined from the culture medium using atomic absorption spectrophotometer.

Fibre compositions (% by weight) A B C SiO₂ 54.7 50.4 59.0 Al₂O₃ 1.7 3.3 0.9 Fe₂O₃ 1.4 3.0 0.3 CaO 25.1 31.2 35.5 MgO 11.9 10.6 4.6 Na₂O 0.3 0.6 0.1 K₂O 0.1 0.4 0.1 P₂O₅ 5.2 — 13

Composition A is in accordance with the invention, compositions B and C otherwise fulfill the conditions of the invention, except that they do not contain any phosphorus.

The diameter of the fibers used in the tests was less than 3 μm.

The following solubility results for silicon were obtained after 2 days, 4 days and 8 days respectively.

Composition A B C Si (ppm; 2 days) Culture medium 26 5 26 -% by weight- + macrophages 26 5 14 Si (ppm; 4 days) Culture medium 45 12 45 -% by weight- + macrophages 45 8 35 Si (ppm; 8 days) Culture medium 162 45 144 -% by weight- + macrophages 153 37 82

From the results it is apparent that the solubility of the composition B, which has a relatively high total content of aluminium and iron oxides, is very low. The composition C, which has a very low total content of aluminium and iron oxides, has a high solubility in culture medium, but a significantly lower solubility in a culture medium containing macrophages.

Fiber A, however, which is according to the invention and which has a considerably higher total aluminium and iron oxide content than the composition C, and which also contains phosphorus, has the same high solubility as the composition C in plain culture medium but, in addition, a correspondingly high solubility also in a culture medium containing macrophages.

The results thus show that in the compositions according to the invention, phosphorus has a solubility increasing effect which is especially pronounced in conditions resembling the true biological conditions in the organism. 

What is claimed is:
 1. Mineral fiber composition which is soluble in biological fluids, consisting essentially of SiO₂ 49-56% by weight Al₂O₃ 0.5-4.2 by weight Fe₂O₃ 0-4 by weight CaO 25-35 by weight MgO  0-15 by weight Na₂O + K₂O 0-6 by weight P₂O₅ 0.5-5   by weight

and the ratio of P₂O₅ to the sum of Al₂O₃ and iron oxide is 0.5 to
 6. 2. The mineral fiber composition according to claim 1, wherein said ratio is 0.5 to
 2. 3. The mineral fiber composition according to claim 2, wherein Al₂O₃ is included in an amount of 1 to 4.2% by weight.
 4. The mineral fiber composition which is soluble in biological fluids, consisting essentially of SiO₂ 49-56% by weight Al₂O₃ 0.5-4.2% by weight Fe₂O₃ 0-4% by weight CaO 25-35% by weight MgO 0-15% by weight Na₂O + K₂O 0-6% by weight P₂O₅ 0.5-5% by weight

and obtained by a method comprising the steps of: preparing the mineral fiber composition with the phosphorus oxide in an amount so that the weight ratio between P₂O₅ compared to the total weight of the Al₂O₃ and iron oxide is 0.5 to 6; and melting and forming the composition by spinning into the mineral fiber.
 5. The composition according to claim 4, wherein the phosphorus oxide is included in the mineral fiber in an amount so that said ratio is 0.5 to
 2. 6. The composition according to claim 4, wherein Al₂O₃ and iron oxide are included in a total amount of 0.5 to 7% by weight. 